I replaced my final stage resistor today following most of your instructions and my fan seems to be operating perfectly. It appears to me that the orignial resistor heat exchanger fins didn't have enough surface area and it overheats. The replacement resistor should run much cooler.

Here's a couple of notes that might help others:
First - remove the ventilation duct. Just pull on it and it will come free. I know this is a tough sell for most do it yourselfers, but I read another web page that said it would come free and being 60 years old and 20 pounds over weight there's no way I was going to get at those screws before freezing in position. The duct mates up easily when you reinstall and a perfect match isn't necessary since it simply directs air to the floor.

Secondly, the little gizmo that you have to remove is the recirculation damper control. Just be careful to note the position of the control arm before you move it and return it to the same spot.